In optical applications, it is often that a light beam must be pointed to a desired projection point through a reflect operation, such as in the applications of Interferometry, Metrology etc. Thus a reflecting mirror is used to reflect an incident light beam and then reflects the incident light beam to a desired projection point. However if the reflecting light beam can not exactly point to the desired projection point, the user must adjust the orientation of the reflecting mirror so as to guide the light beam to the projection point. Because it is required that the light beam to point the projection point with a very high precision, adjustment of the orientation of the reflecting mirror must be very precise.
A prior way for adjusting the orientation of the reflecting mirror is illustrated in the FIGS. 1A and 1B. In the following, the elements of this prior art structure will be described.
A reflecting mirror 20 serves to reflect incident light beam C and generate a reflecting light beam R to a desired projection point P. Generally, the reflecting light beam R can not firstly point to the desired projection point P so that the user must adjust the orientation of the reflecting mirror 20 to cause the reflecting light beam R to the desired projection point P.
A retaining plate 10 serves for fixing the reflecting mirror 20.
An adjusting plate 30 is located at the backside side of the retaining plate 10.
In this case, the retaining plate 10 is formed with a recess 11 and the adjusting plate 30 is formed with another recess 33. The retaining ball 40 is fixed between the recess 11 of the retaining plate 10 and the recess 33 of the adjusting plate 30.
A retaining spring 50 is fixed between the retaining plate 10 and the adjusting plate 30. The retaining spring 50 has the effect of pulling the retaining plate 10 and the adjusting plate 30 to be closer, while the retaining ball 40 cause that the retaining plate 10 and the adjusting plate 30 to be retained in a predetermined distance; and thus the structure formed by the retaining plate 10, the adjusting plate 30, the retaining ball 40 and the retaining spring 50 is retained in a fixed relation.
As above mentioned, it is desired to adjust the orientation of the reflecting mirror 20 slightly so that the reflecting light beam R moves to a desired point P. A first adjusting screw 60 has one end resisted against the reflecting plate 10 and a section of the first adjusting screw 60 is threadedly engaged to the threaded hole 32 of the adjusting plate 30, while another end of the first adjusting screw 60 exposed out of a backside of the adjusting plate 30. In adjusting, as the user adjusts the first adjusting screw 60, it will cause the retaining plate 10 and the adjusting plate 30 to move close or away from each other.
However in above mentioned prior art, due to the sensitivity of the hand of the user, each moving step of the adjusting screw 60 is confined. As a result, it is often that the step moving distance is above several micrometers. However this step distance is too large so that the user can not well control the reflecting direction of the reflecting light beam R which induces the difficult in adjustment.